1. Field of the Invention
This invention relates to method for forming a contoured die suitable for stamping heat exchange channel element wall members from thin sheet metal, and to the contoured die produced thereby.
2. Description of the Prior Art
A number of industrial heat exchange applications have created a demand for lightweight, inexpensive heat exchangers formed from thin-walled heat exchange channel elements. In U.S. Pat. No. 3,757,856 to L. C. Kun, a lightweight, potentially inexpensive heat exchange channel element is disclosed which can be used to fabricate a heat exchanger of exceptional strength and excellent heat transfer performance characteristics. The Kun heat exchanger comprises an array of parallel channels formed of thin heat conductive walls which have on their surface osostress contours with uniformly disposed unidirectional wall-supporting projections formed from the wall.
U.S. Pat. No. 4,024,623 to L. C. Kun discloses a method of forming a stamping die with which heat exchange walls for channel elements of the above-mentioned type can be fabricated from thin sheet metal. This method involves the deformation of a flexible membrane into the desired isostress surface configuration by by pneumatic pressure differential across the membrane, with deposition and subsequent setting of a curable material on the deformed flexible membrane. The cured material having the isostress-contoured surface configuration is then ready to be used as a die.
An improvement to the pneumatically deformed membrane die-making method described above is disclosed in U.S. Pat. No. 4,133,227 to J. J. Crowe et al. This patent discloses method of fabricating a metal die having an isostress-contoured surface configuration by direct machining of a metal workpiece.
The isostress-contoured heat exchange surface produced by stamping thin sheet metal with dies manufactured in accordance with the foregoing methods, despite their high strength and heat transfer capability, have not yet been widely implemented in practice. A primary reason for this lack of implementation is the significant pressure drop which is associated with the heat transfer fluid flowed over the isostress-contoured surface, particularly when same is employed in a stacked channel element heat exchanger, e.g., automobile radiators. It has recently been determined that the substantial advantages of the isostress-contoured heat exchange surface can be retained while markedly reducing the external fluid medium pressure drop characteristic associated therewith by a heat exchange wall member having wall projection portions extending elongately on the wall member surface, with the elongated projections being oriented on the wall member surface substantially parallel to one another and with adjacent projections being separated by concavely curved wall surface portions. The surface of heat exchange wall members with such configuration is hereinafter referred to as a "ridge projection" surface.
Accordingly, it is an object of the present invention to provide a metal die suitable for stamping heat exchange wall members having a ridge projection wall surface from thin sheet metal, and to provide a method of fabricating such a die.